Monolithically integrated thin-film electronic conversion unit for lateral multijunction thin-film solar cells

ABSTRACT

An integrated thin-film lateral multi-junction solar device and fabrication method are provided. The device includes, for instance, a substrate, and a plurality of stacks extending vertically from the substrate. Each stack may include layers, and be electrically isolated against another stack. Each stack may also include an energy storage device above the substrate, a solar cell above the energy storage device, a transparent medium above the solar cell, and a micro-optic layer of spectrally dispersive and concentrating optical devices above the transparent medium. Furthermore, the device may include a first power converter connected between the energy storage device and a power bus, and a second power converter connected between the solar cell and the power bus. Further, different solar cells of different stacks may have different absorption characteristics.

PRIOR FOREIGN APPLICATION

This application is a continuation of application Ser. No. 14/805,833,filed 22 Jul. 2015, which claims priority to the United Kingdom PatentApplication No. GB1417577.2, filed Oct. 6, 2014. The contents of U.S.application Ser. No. 14/805,833 and United Kingdom Patent ApplicationNo. GB1417577.2 are hereby incorporated by reference in theirentireties.

BACKGROUND

The invention relates generally to an integrated thin-film lateralmulti-junction solar device. The invention relates further to a relatedmethod of building an integrated thin-film lateral multi-junction solardevice.

Solar cells are photovoltaic devices which convert sunlight intoelectricity. Solar cells are either made of crystalline silicon wafersor are based on thin-film silicon technologies. Alternatively, solarcells may be based on amorphous silicon. Other alternatives may be basedon CIGS (Copper-Indium-Gallium-(Di-(Selenide)), CdTe (Cadmium-Telluride)or CZTS (Copper-Zinc-Tin-Sulfide). Solar cells are used in a wide rangeof applications. They may, for example, be used to deliver power into apublic power grid, recharge batteries in remote locations, rechargemobile devices like mobile telephones, or may function as a sole energysource for pocket calculators. One key design parameter for solar cellsis the production price in relation to the efficiency of the conversionprocess from light energy to electrical energy.

In order to maximize the energy yield from photovoltaic conversion, thehighest efficiencies are reached by multi-junction solar cells, andreaching efficiencies over 45% so far. In order to simplify the requiredoptimization of optical and electrical properties, lateralmulti-junction solar cells are a means to separate the radiationspectrum into spectrum bands most suitable for a material system with aband-gap optimized for a spectrum band. Lateral multi-junction solarcells have a series of individual solar cells placed side by side on asubstrate, each solar cell with differing characteristics such asmaterial composition, band-gaps, absorption and diode characteristics.In the standard configuration, individual sub-cells are connected inseries, reducing the overall efficiency with the worst performing diodecharacteristics. This is a major drawback to traditional multi-junctionsolar cells.

SUMMARY

The above-mentioned solar cells do not integrate energy storing devicesand/or power converters for best energy harvesting. Hence, there is aneed for cost effective ways to optimize connection pattern of sub-cellsfrom the multiple lateral photovoltaic junctions, and thus, optimizingthe overall efficiency and energy yield from a multi-junction solarcell.

This need may be addressed by an integrated thin-film lateralmulti-junction solar device, and a method of building a relatedintegrated thin-film lateral multi-junction solar device according tothe independent claims. Advantageous embodiments are described in thedependent claims.

According to one aspect, an integrated thin-film lateral multi-junctionsolar device may be provided. The device may comprise a substrate and aplurality of stacks extending vertically from the substrate. Each stackmay comprise layers, wherein each stack is electrically isolated againstanother stack. Each stack may comprise an energy storage device abovethe substrate, a solar cell above the energy storage device, atransparent medium above the solar cell, and a micro-optic layer ofspectrally dispersive and concentrating optical devices above thetransparent medium. Moreover, the device may comprise a first powerconverter connected between the energy storage device and a power bus,and a second power converter connected between the solar cell and thepower bus, wherein different solar cells of different stacks havedifferent absorption characteristics.

According to another aspect, a method of building an integratedthin-film lateral multi-junction solar device may be provided. Themethod may comprise providing a substrate and forming a plurality ofstacks extending vertically from the substrate. Each stack may compriselayers. The method may also comprise forming a vertical isolator on thesubstrate between the stacks. Each stack may be built by forming anenergy storage device above the substrate, forming a first powerconverter and building conductors for connecting the energy storagedevice to the first power converter and for connecting the first powerconverter to a power bus, forming a solar cell above the energy storagedevice, forming a second power converter and building conductors betweenthe solar cell and the second power converter and for connecting thesecond power converter to the power bus. Moreover, the method maycomprise forming a transparent medium above the solar cell, and forminga micro-optic layer of spectrally dispersive and concentrating opticaldevices above the transparent medium, such that different solar cells ofdifferent stacks have different absorption characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention are described below, by way ofexample only, with reference to the following drawings:

FIG. 1 shows a block diagram of an embodiment of an inventive integratedthin-film lateral multi-junction solar device, in accordance with one ormore aspects of the present invention;

FIG. 2 shows a block diagram of an embodiment of an integrated thin-filmlateral multi-junction solar device in cross-sectional view, inaccordance with one or more aspects of the present invention;

FIG. 3 shows a logical block diagram of a group of integrated thin-filmlateral multi-junction solar devices, in accordance with one or moreaspects of the present invention;

FIG. 4 shows an embodiment of circuitries of power converters with solarcells and energy storage devices, in accordance with one or more aspectsof the present invention;

FIG. 5 shows a 3-dimensional view of an arrangement of severalintegrated thin-film lateral multi-junction solar devices, in accordancewith one or more aspects of the present invention; and

FIG. 6 shows a flow-diagram of a method of building an integratedthin-film lateral multi-junction solar device, in accordance with one ormore aspects of the present invention.

DETAILED DESCRIPTION

It may be noted that for the micro-optics device also a concentrationfactor of 1 would be possible resulting in no concentration of incomingradiation. It also should be noted that all elements of an integratedthin-film lateral multi-junction solar device may be monoliticallyintegrated.

In the context of this description, the following conventions, termsand/or expressions may be used:

The term “lateral multi-junction solar device” may denote a system ofseveral photovoltaic devices that may be arranged side by side in anisolated way on a substrate. The term multi-junction may denote thatmore than one pn-junction is present, wherein different pn-junctionsgenerate electrical power based on incoming radiation with differentwavelength and thus, different energy.

The term “energy storage device” may denote a storage device for storingelectrical power. Several technologies may be used. Typical technologiesfor storing electrical energy may comprise a thin-film battery, a3-dimensional thin-film battery and a super-capacitor.

The term “solar cell” may denote a semiconductor device—in particular adiode comprising a pn-junction—adapted for converting radiation energyinto electrical energy.

The term “micro-optic layer” may denote a layer—in particular an outerlayer—of a semiconductor device. The micro-optic layer may be adoptedfor a diffraction or a refraction of incoming radiation, i.e., light.

The term “power converter” may denote an electrical circuitry totransform voltage levels from one level to another one. One option toimplement a power converter is a switching converter. The converter maywork in both directions, e.g., from an energy source, e.g., anelectrical storage device to a power bus and vice versa.

The term “absorption characteristics” may denote that a solar cell mayabsorb energy of different wavelength with a different efficiency. Theabsorption may be related to the energy band-gap of the involvedsemiconductor. Different semiconductors may have different band-gaps.Certain compound semiconductors may have varying band-gaps, depending onthe percentages of their components. One example is a spatiallycomposition-graded Cd_(x)Pb_(1-x)S compound material.

The term “superstate” or “superstrate configuration” may denote a solarcell at which incoming radiation enters an active layer through thesupporting substrate of the solar cell. This is in contrast to asubstrate configuration in which incoming radiation enters the activelayer from a direction opposite to the substrate, i.e., from the top ofthe device.

In one or more aspects, the proposed integrated thin-film lateralmulti-junction solar device offers a number of advantages:

For instance, in one or more embodiments, different active layers ofmulti-junction solar cells may be independent from each other. Thus, ahigh-performance solar cell may not be influenced negatively in itspower output by a low-performing solar cell because the individualactive layers of the solar cells are electrically decoupled. Each activelayer may be connected to a separate power converter which may deliverits output to a joint power bus. The active layers of the solar cells,i.e., the diodes or pn-junctions may not be connected in series suchthat the lowest performing device determines the power output of thecombined device. Energy harvesting of multi-junction solar cells may beenhanced significantly. The characteristics of the different devices maybe decoupled from each other by the power bus and the related powerconverters.

Also, in one or more embodiments, generated electrical power from thesolar cells may be stored directly into the solar device. This may builda basis for a more constant power output in environments with varyingincoming radiation, i.e., incoming light.

As refractive and/or diffractive elements, commercially availableelements may be used and allowing a cost-effective production of theintegrated thin-film lateral multi-junction device.

According to one embodiment of the integrated thin-film lateralmulti-junction solar device, the different absorption characteristics ofthe different solar cells may be based on different energy band-gaps ofsemiconductors building the solar cells, in particular such that thedifferent solar cells are sensitive to different wavelength of incomingradiation. The available radiation of a given wavelength may be directedto the solar cell with a compatible band-gap. This may increase theoverall efficiency of the solar device.

According to a further embodiment of the integrated thin-film lateralmulti-junction solar device, the micro-optic layer may be a combinationof refractive and/or diffractive optical elements. This may allow for anoptimal correlation of available radiation of a given wavelength tophotovoltaic cell having “the right”, corresponding band-gap.

According to an enhanced embodiment of the integrated thin-film lateralmulti-junction solar device, the combination of refractive and/ordiffractive optical elements is at least one of a Fresnel lense, aprism, a holographic optical device and a grating. In one practicalimplementation, it may be a plurality of each of those elements, or acombination thereof.

According to an advantageous embodiment of the integrated thin-filmlateral multi-junction solar device, the integrated thin-film lateralmulti-junction solar device has either a superstrate or a substrateconfiguration. This may allow a high degree of freedom in the design ofthe solar device.

According to one embodiment of the integrated thin-film lateralmulti-junction solar device, the energy band-gap of the solar cell ofeach one of the stacks is selected according to the wavelength ofradiation transmitted from the micro-optic layer to the solar cell suchthat an optimum of energy conversion from radiation energy to electricalenergy is achieved. In each of the solar cells of a plurality of stackscomprising several active photovoltaic devices, they may each receive anoptimality adapted radiation and maximum of power harvesting may beachieved.

According to one embodiment of the integrated thin-film lateralmulti-junction solar device, the energy storage device may comprise atleast a conducting bottom lead, a bottom electrode, a charge storagemedium, a top electrode and a conducting top lead. Such an energystorage device may have a solid characteristic and proven productionprocesses may be used. The energy storage device may be arranged on topor below an active photovoltaic device of the solar device.Additionally, the solar device may comprise a plurality of stackedenergy storage devices. Either the complete stack or individual cells ofthe energy storage device may be linked to a related power converter.

Advantageously, the energy storage device comprises at least one of athin-film battery, a 3-dimensional thin-film battery or asuper-capacitor. This may give design freedom in the construction of thesolar device.

According to a further embodiment of the integrated thin-film lateralmulti-junction solar device, the first power converter and/or the secondpower converter may comprise at least thin-film resistive, capacitiveand/or inductive elements, as well as electronic components in thin-filmtechnology. Thus, the power converters may use conventional active andpassive elements which may be manufactured in thin-film technology.

According to an exemplary embodiment of the integrated thin-film lateralmulti-junction solar device, the solar cell may be a solar cell diode.This may represent a common implementation of the solar cell. Anyknown-technology for building pn-junctions with adaptable band-gaps maybe used.

According to an advantageous embodiment of the integrated thin-filmlateral multi-junction solar device, the first power converter may betightly integrated with a layer of the energy storage device. “Tightlyintegrated” may denote that the layer of the first power converter andlayers of the energy storage device may be close to each other in aphysical sense. This may mean that the first power converter may bemanufactured directly on top of the energy storage device. It may alsomean that the energy storage device and the first power converter may bestacked on each other as a three-dimensional device, wherein differentlayers of the device may be connected to each other through vias.

It may also be mentioned that the solar device connections betweendifferent layers of the solar device may be achieved by vias throughother layers, which may be conducted on nonconductive layers. The viasmay be isolated against the intermediate other layers.

It may also be noted that the circuitry of the first power converter maybe arranged side-by-side with the energy storage device in laterallydistinctive areas of the same physical layer. In a related sense, thesame may be applicable to the second power converter and the relatedsolar cell.

According to a further advantageous embodiment of the integratedthin-film lateral multi-junction solar device, the second powerconverter may be tightly integrated with a layer of the solar cell. Asdiscussed in the context of the energy storage device and the firstpower converter, also for the second power converter and the relatedsolar cells a series of different design options may be available.

It should also be noted that embodiments of the invention are describedherein with reference to different subject-matters. In particular, someembodiments are described with reference to method type claims, whereasother embodiments are described with reference to apparatus type claims.However, a person skilled in the art will understand that, unlessotherwise specified, in addition to any combination of featuresbelonging to one type of subject-matter, also any combination betweenfeatures relating to different subject-matters, in particular, betweenfeatures of the method type claims, and features of the apparatus typeclaims, is considered as to be disclosed within this document.

The aspects defined above and further aspects of the present inventionare apparent from the examples of embodiments described hereinafter, andare explained with reference to certain exemplary embodiments, but towhich the invention is not limited.

In the following, a detailed description of the figures is given. Notethat instructions in the figures are schematic. Firstly, a block diagramof an embodiment of the inventive integrated thin-film lateralmulti-junction solar device is given. Afterwards, further embodimentsand the method for building the inventive integrated thin-film lateralmulti-junction solar device will be described.

FIG. 1 shows a block diagram of one embodiment of an integratedthin-film lateral multi-junction solar device 100, where verticallyextending stacks 122, 124, 126 are built on a substrate 102. Each stackcomprises a plurality of layers 104 to 118, and each stack 122, 124, 126is vertically electrically isolated against another stack. Ifconnections between sub-layers of the layers 102 to 118 may be required,conventional technologies, like vias, may be used.

The lowest layer above substrate 102 may be an energy storage device104. Atop, but electrically isolated from the energy storage device 104by an isolator 108, may be a solar cell 110. Vias (not shown) mayprovide the required electrical connections.

A first power converter 106 may be connected between the energy storagedevice 104 and a power bus 120. In FIG. 1, the first power converter 106is shown side-by-side with the energy storage device 104. However, thepower converter 106 may also be positioned above the power storagedevice 104 in another layer of one of the stacks 122, 124, 126.

The same applies to the solar cell 110 and the second power converter112. They are shown side-by-side, but may also be implemented on top ofeach other. The second power converter 112 may also be connected topower bus 120. It may be noted that details of the power bus 120 are notshown in this figure.

On top of solar cell 110 an insulator layer 114 and another transparentlayer 116 are shown. The insulator layer 114 and transparent layer 116may ensure, that a micro-optic layer 118 of optically spectrallysplitting and concentrating devices, may have an appropriate distance tothe solar cell, such that a splitting of radiation of differentwavelengths may be directed to one of the solar cells 110 in one of thestacks 122, 124, 126. The size of the micro-optic device may be in therange of 10 . . . 10,000 μm.

It may be noted that more than three vertical stacks 122, 124, 126 maybe arranged side-by-side with solar cells sensitive to differentwavelength of the incoming light. It may also be noted that the device100 may be a substrate configuration. In case of a superstrateconfiguration, the incoming light may enter the solar device from belowthe substrate 102. In that case, the micro-optic layer 118 may bearranged below the substrate 102. Also the sequence of the layers 104 to116 may be arranged differently in a superstrate configuration.

It may also be mentioned that the power bus 120 is only shownsymbolically as a block beside the other layers. However, in otherimplementations may be possible, e.g., as an integrated layer within thestacks 122, 124, 126. The power converters may be DC/DC powerconverters.

It may be noted that only the layer 122 has reference numerals. Askilled person will be able to extend the reference numeral scheme tothe other two shown stacks 124, 126, that are shown by way of example ofa plurality of stacks. Note also that the energy storage devices 104 ofthe different stacks 122, 124, 126 may be loaded with power from thesolar cells 110.

FIG. 2 shows a block diagram of one embodiment of an integratedthin-film lateral multi-junction solar device in cross-sectional view200. On substrate 102, an energy storage device is shown comprising alower contact 202, an upper contact 206 and an energy storage layer 204.On top of the energy storage device isolator 108 of FIG. 1 is shown.

It may also be mentioned that reference numerals have only been drawnfor the most left stack. In one or more embodiments, the middle andright stacks in FIG. 2 differentiate themselves only by differentband-gaps of the corresponding absorbers 210. This is expressed by thedifferent wavelengths λ₁, λ₂, λ_(n) indicating that incoming radiationmay be split by the micro-optic layer of spectrally dispersive andconcentrating optical devices 118 to be directed to one of the solarcells sensitive for a specific wavelength λ₁, λ₂, λ_(n). A skilledperson will also understand that the distance shown between the energystorage device 104 and the solar cell 110 in FIG. 2 is a result of theschematic form of the figure and for writing additional referencenumerals in the gap. However, in reality, the layers would be close toeach other but isolated.

The solar cell in each stack comprises at least a lower contact 208, theabsorber 210 for a specific band-gap, an n-type semiconductor 212 and anupper transparent conducting oxide 214 (TCO, e.g., ITO=Indium Tin Oxideor Zinc oxide). It may also be seen from FIG. 2 that individual stacksof energy storage devices and solar cells may be vertically isolatedagainst each other. Horizontal dots 214 between stacks may indicate thatnumerous vertical stacks may be possible building one integratedthin-film lateral multi-junction solar device. The dots 216 may denotethat a plurality of such integrated thin-film lateral multi-junctionsolar devices may be cascaded side by side building a module ofintegrated thin-film lateral multi-junction solar devices.

FIG. 3 shows a logical block diagram of a group of stacks 300 of anintegrated thin-film lateral multi-junction solar device or severalintegrated thin-film lateral multi-junction solar devices. Each stack ofthe plurality of integrated thin-film lateral multi-junction solardevices is denoted as 302, 304, 306 and repeat-units. FIG. 3 should makeclear that every stack has its related first and second power converterswhich are each connected to a power bus 120.

FIG. 4 shows an embodiment of circuitries of power converters with solarcells and energy storage devices. Solar cells 402, 406, 410 sensitive towavelength λ₁, λ₂, λ_(n) due to varying band-gaps are connected to asecond power convertor, which is connected to the power bus 120. Relatedto every solar cell 402, 406, 410 there may be an energy storage device404, 408, 412, which may be connected to a first power convertor whichmay also be connected to the power bus 120.

It may be appreciated that n may be >2. Depending on the number ofspectral bands, the micro-optic device may split the incoming radiation.The first and second power converters may comprise a plurality of activeand passive electronic elements in thin film technology, liketransistors, resistors, capacitors and inductors as required for atypical power converter.

FIG. 5 shows a 3-dimensional view of an arrangement of severalintegrated thin-film lateral multi-junction solar devices eachcomprising a plurality of stacks 122, 124, 126, and each being sensitiveto a different wavelength. Several such thin-film lateral multi-junctionsolar devices (device 1, device 2, device 3) may be placed side-by-sidebuilding a larger module 502 of thin-film lateral multi-junction solardevices.

FIG. 6 shows a method 600 of building an integrated thin-film lateralmulti-junction solar device. Steps of the method may comprise providing,602, a substrate 102 and forming a plurality of stacks extendingvertically from the substrate. Each stack comprises layers, and eachstack may be built by forming, 606, an energy storage device above thesubstrate and forming, 608, a first power converter and buildingconductors for connecting the energy storage device to the first powerconverter and for connecting the first power converter to a power bus.Furthermore, the method 600 may comprise forming, 610, a solar cellabove the energy storage device, forming, 612, a second power converterand building conductors between the solar cell and the second powerconverter, as well as between the second power converter and the powerbus.

Additionally, the method may comprise forming, 614, a transparent mediumabove the solar cell and forming, 616, a micro-optic layer of spectrallydispersive and concentrating optical devices above the transparentmedium, such that different solar cells of different stacks havedifferent absorption characteristics. The different absorptioncharacteristics may be related to being sensitive to incoming radiationof different wavelength due to different band-gaps of the active layerof the solar cell.

The method 600 may also comprise forming 604 vertical isolators on thesubstrate between the stacks.

Required electrical connections between layers or sub-layers of thesolar device may be achieved by vias.

While the invention has been described with respect to certainembodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments may be devised, whichdo not depart from the scope of the invention, as disclosed herein.Accordingly, the scope of the invention should be defined by theattached claims. Also, elements described in association with differentembodiments may be combined.

Aspects of the present disclosure are described with reference toflowchart illustrations and/or block diagrams of methods and apparatus(devices) according to embodiments of the present disclosure. It will beunderstood that each block of the flowchart illustrations and/or blockdiagrams, and combinations of blocks in the flowchart illustrationsand/or block diagrams, may be implemented in different orders from thoseshown.

The block diagrams in the Figures illustrate the architecture,functionality, and operation of possible implementations of systems andmethods, according to various embodiments of the present disclosure. Itshould also be noted that, in some alternative implementations, thefunctions, discussed hereinabove, may occur out of the disclosed order.For example, two functions taught in succession may, in fact, beexecuted substantially concurrently, or the functions may sometimes beexecuted in the reverse order depending upon the functionality involved.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to limit the invention. As usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will further be understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or steps plus function elements in the claims below are intendedto include any structure, material, or act for performing the functionin combination with other claimed elements, as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimiting to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skills in the artwithout departing from the scope and spirit of the invention. Theembodiments depicted were chosen and described in order to explain theprinciples of the invention and the practical application, and to enableothers of ordinary skills in the art to understand the invention forvarious embodiments with various modifications, as are suited to theparticular use contemplated.

What is claimed is:
 1. A method of building an integrated thin-filmlateral multi-junction solar device, comprising: providing a substrate,forming a plurality of stacks extending vertically from the substrate,each stack comprising layers, forming a vertical isolator on thesubstrate between the stacks, wherein each stack is built by forming anenergy storage device above the substrate, forming a first powerconverter and building conductors for connecting the energy storagedevice to the first power converter and for connecting the first powerconverter to a power bus, forming a solar cell above the energy storagedevice, forming a second power converter and building conductors betweenthe solar cell and the second power converter and for connecting thesecond power converter to the power bus, forming a transparent mediumabove the solar cell, and forming a micro-optic layer of spectrallydispersive and concentrating optical devices above the transparentmedium, wherein different solar cells of different stacks have differentabsorption characteristics.
 2. The method of claim 1, wherein thedifferent absorption characteristics of the different solar cells arebased on different energy band-gaps of semiconductors building the solarcell.
 3. The method of claim 1, wherein the micro-optic layer is acombination of refractive and/or diffractive optical elements.
 4. Themethod of claim 3, wherein the combination of refractive and/ordiffractive optical elements is at least one of a Fresnel lens, a prims,a holographic optical device and a grating.
 5. The method of claim 1,wherein the energy band-gap of the solar cell of each one of the stacksis selected according to the wavelength of radiation transmitted fromthe micro-optic layer to the solar cell such that an optimum of energyconversion from radiation energy to electrical energy is achieved. 6.The method of claim 1, wherein the energy storage device comprises atleast a conducting bottom lead, a bottom electrode, a charge storagemedium, a top electrode and a conducting top lead.
 7. The method ofclaim 1, wherein the energy storage device comprises at least one of athin-film battery, a 3-dimensional thin-film battery or asuper-capacitor.
 8. The method of claim 1, wherein the first powerconverter and/or the second power converter comprises at least thin-filmresistive, capacitive and/or inductive elements, as well as electroniccomponents in thin-film technology.